Pre-APFS OS on a APFS drive?

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Pre-APFS OS on a APFS drive?

I’ve been trying to understand how the new APFS formatting works, but I’m afraid it’s got my mind blown. So please forgive the immediate resort to asking what is probably a simple question here.

SHORT VERSION: Can I take a drive that is already formatted APFS with Catalina, partition it, and install El Capitan or Sierra on the new partition?

LONG VERSION: I recently got a used 2014 Mini so I could run some legacy software. It came pre-installed with Catalina, and I want to keep it for those times I need a (relatively) modern OS.

But I need to also run either El Capitan or Sierra on this machine for some older audio software.

If it’s possible, I’d like to partition the existing internal drive. But I don’t know if one can keep a drive formatted for APFS and install an older pre-APFS operating system on it.

If not, I’ll get myself a blade SSD as a second physical drive, but for the time being I’d like to skip the expense.

Thanks in advance and going forward for all replies.

Posted on Jun 16, 2023 2:46 PM

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Answer 1

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a brody

Level 10

84,055 points

Jun 17, 2023 9:40 AM in response to kenlac

Yes, if you have the space constraints, and the system you are using is able to run both operating systems. You need to create a separate HFS Extended GUID partition for the operating systems older than High Sierra. And your Mac Mini meets the second criteria. The big question is how big is the drive on your Mac Mini.

Worst case scenario you could attach an external hard drive with the older operating system installed on it.

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Answer 2

kenlac Author

Level 1

8 points

Jun 17, 2023 11:58 PM in response to a brody

Success! Thank you so much. I am now happily running Sierra on one half of the drive, and Catalina on the other.

I will note for others who may be reading later: for some strange reason, I had to take a specific additional step before the OS install apps would allow me to target the new partition: after using Catalina’s Disk Utility to create the new partition, I had to then erase the new partition again in order to get the option to make it journaled. I’m not sure why it didn’t format as journaled the first time.

I had absolutely no luck creating a bootable USB thumb-drive installer, but I was able to get the job done using some other resources I had around.

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Pre-APFS OS on a APFS drive?

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